From German Offenlegungsschrift No. 2334492 it is known in such rolling mills to measure the pressure applied by the working rolls and the width of the material being rolled in order to obtain a signal for the optimum intermediate roll position and the optimum crown force. These measuring signals are used in a mathematical model of the rolling mill in order to obtain the correct regulating signal. Thus this prior invention is dependent on a mathematical operation and use is not made of any measurement of the flatness of the rolled material.
It is also known from U.S. Pat. No. 3,534,571 to measure the roll pressure and, while using this measured value, to control the crown of the working rolls in a four-high rolling mill. However, with this arrangement problems may also arise in obtaining a truly flat end product, since again no direct measurement of the flatness of the rolled product is made.
The present invention aims to provide a solution to the above-mentioned problems and other problems associated therewith in connection with a rolling mill of the above-described kind.